Effect of negative self-bias voltage on microstructure and properties of DLC films deposited by RF glow discharge

Influence of system parameters such as RF power and discharge pressure on the negative self-bias voltage of substrate was systematically investigated by Oscilloscope with a high voltage probe. It is found that the self-bias voltages increase linearly with the square root of RF power, and decrease with the discharge pressure at both pure argon gas and gas mixture of argon and acetylene, and the self-bias voltages increase with the ratio of acetylene. Moreover, the hydrogenated amorphous carbon films were deposited by RF glow discharge at input RF power of 500 W and 700 W. The microstructure and mechanical properties of these a-C:H films were investigated via Raman spectroscopy and Nano-indentation technique. The ID/IG ratio of a-C:H films deposited at 500 W (its value is 0.66) is lower than that of film deposited at 700 W (its value is 1.14). This implies that there is a higher fraction of sp3 bonding in the film prepared at 500 W, and this trend is confirmed by the results of Nano-indentation test.